This is the 10501st most frequent Russian word.
взявшийся
"Having undertaken" or "having taken up."
In this sentence, 'взявшийся' describes someone who has undertaken or started doing the task, highlighting the assumed responsibility.
Неизвестно, кто взявшийся за эту задачу.
It is unknown who has taken up this task.
Here, 'взявшийся' emphasizes the initiative of the student, indicating that they began actively working on the task.
Взявшийся за работу студент показал хорошие результаты.
The student who took up the work showed good results.
In this instance, 'взявшийся' refers to the collective action by participants beginning the project, underlining shared effort.